An intermittent rocking platform for integrated expansion and differentiation of human pluripotent stem cells to cardiomyocytes in suspended microcarrier cultures

Abstract

The development of novel platforms for large scale production of human embryonic stem cells (hESC) derived cardiomyocytes (CM) becomes more crucial as the demand for CMs in preclinical trials, high throughput cardio toxicity assays and future regenerative therapeutics rises. To this end, we have designed a microcarrier (MC) suspension agitated platform that integrates pluripotent hESC expansion followed by CM differentiation in a continuous, homogenous process. Hydrodynamic shear stresses applied during the hESC expansion and CM differentiation steps drastically reduced the capability of the cells to differentiate into CMs. Applying vigorous stirring during pluripotent hESC expansion on Cytodex 1 MC in spinner cultures resulted in low CM yields in the following differentiation step (cardiac troponin-T (cTnT): 22.83 ± 2.56%; myosin heavy chain (MHC): 19.30 ± 5.31%). Whereas the lower shear experienced in side to side rocker (wave type) platform resulted in higher CM yields (cTNT: 47.50 ± 7.35%; MHC: 42.85 ± 2.64%). The efficiency of CM differentiation is also affected by the hydrodynamic shear stress applied during the first 3 days of the differentiation stage. Even low shear applied continuously by side to side rocker agitation resulted in very low CM differentiation efficiency (cTnT < 5%; MHC < 2%). Simply by applying intermittent agitation during these 3 days followed by continuous agitation for the subsequent 9 days, CM differentiation efficiency can be substantially increased (cTNT: 65.73 ± 10.73%; MHC: 59.73 ± 9.17%). These yields are 38.3% and 39.3% higher (for cTnT and MHC respectively) than static culture control. During the hESC expansion phase, cells grew on continuously agitated rocker platform as pluripotent cell/MC aggregates (166 ± 88 × 105 μm2) achieving a cell concentration of 3.74 ± 0.55 × 106 cells/mL (18.89 ± 2.82 fold expansion) in 7 days. These aggregates were further differentiated into CMs using a WNT modulation differentiation protocol for the subsequent 12 days on a rocking platform with an intermittent agitation regime during the first 3 days. Collectively, the integrated MC rocker platform produced 190.5 ± 58.8 × 106 CMs per run (31.75 ± 9.74 CM/hESC seeded). The robustness of the system was demonstrated by using 2 cells lines, hESC (HES-3) and human induced pluripotent stem cell (hiPSC) IMR-90. The CM/MC aggregates formed extensive sarcomeres that exhibited cross-striations confirming cardiac ontogeny. Functionality of the CMs was demonstrated by monitoring the effect of inotropic drug, Isoproterenol on beating frequency. In conclusion, we have developed a simple robust and scalable platform that integrates both hESC expansion and CM differentiation in one unit process which is capable of meeting the need for large amounts of CMs.